1. Field of the Invention
The present invention relates to field programmable gate array (FPGA) devices. More particularly, the present invention relates to FPGA integrated circuits employing flash memory as the programming medium and to providing radiation resistant flash FPGA integrated circuits.
2. The Prior Art
FPGA integrated circuits are well known in the art. The programming mechanisms for FPGA devices include antifuses, static random access memory (SRAM) devices and flash memory. Flash memory based FPGA integrated circuits usually comprise one or more floating gate flash MOS transistors. The one or more floating gate flash MOS transistors are used to drive the gate of a transistor programming switch that selectively interconnects desired circuit nodes.
When these prior-art flash-based FPGA devices are subjected to radiation, the charge stored on the floating gates of the flash transistors slowly leaks off, thus gradually degrading the drive signal provided to the transistor switch that is used to make the desired interconnection. The effect of radiation exposure on the floating gate flash transistors is cumulative. After a sufficient exposure to radiation, enough charge has leaked from the floating gates of the flash transistors so that the state of the switching transistor cannot be guaranteed.